Exhaust Systems and Methods of Assembling Exhaust Systems for Marine Propulsion Devices

ABSTRACT

An exhaust system is for a marine propulsion device having an internal combustion engine. A catalyst housing has a housing inlet end that receives an exhaust gas flow from the internal combustion engine into the catalyst housing and an opposite, housing outlet end that discharges the exhaust flow out of the catalyst housing. A catalyst is disposed in the catalyst housing. The catalyst has a catalyst inlet end that receives the exhaust gas flow and an opposite, catalyst outlet end that discharges the exhaust gas flow. A catalyst mantel is on an outer periphery of the catalyst. The catalyst mantel has a mantel inlet end and an opposite, mantel outlet end. A radial flange is on at least one of the mantel outlet end and mantel inlet end. A connector mates with an inner diameter of the catalyst housing. The radially extending flange of the catalyst mantel is axially sandwiched between the connector and a radially inner shoulder of the catalyst housing.

FIELD

The present disclosure relates to exhaust systems and methods ofassembling exhaust systems for marine propulsion devices having aninternal combustion engine.

BACKGROUND

The following U.S. patent and patent applications are incorporatedherein by reference, in entirety.

U.S. patent application Ser. No. 14/521,797 discloses a marinepropulsion device having an internal combustion engine that dischargesexhaust gases, a driveshaft housing that is located vertically below theengine, and a catalyst that is sandwiched between opposing castings ofthe device that face each other at a split-line. The exhaust gases flowthrough the catalyst parallel to the split-line.

U.S. patent application Ser. No. 14/543,453 discloses an outboard marinepropulsion device that comprises an internal combustion engine having acylinder head and a cylinder block, and an exhaust manifold thatdischarges exhaust gases from the engine towards a vertically extendingcatalyst housing. The exhaust manifold has a plurality of horizontallyextending inlet runners that receive the exhaust gases from the engine,and a vertically extending collecting passage that conveys the exhaustgases from the plurality of horizontally extending inlet runners to abend that redirects the exhaust gases downwardly towards the catalysthousing.

U.S. Patent Application Publication No. 2008/0166935 discloses anoutboard motor that includes a multi-cylinder engine which includescylinders longitudinally oriented and vertically paralleled in acylinder block, a cylinder head arranged at a rearward position of thecylinder blocks, and a crankcase arranged at a forward position of thecylinder block, the cylinder head having an outlet of an exhaust port atone side thereof. An exhaust system for the outboard motor includes anexhaust manifold which communicates the outlet of the exhaust port withan exhaust outlet opening, the exhaust manifold including a firstexhaust gas passage extending in a vertical direction for gatheringexhaust gas discharged from the outlet of each exhaust port and a secondexhaust gas passage extending in a vertical direction adjacently to thefirst exhaust gas passage. A catalyst unit is provided on the way of thesecond exhaust gas passage.

U.S. Pat. No. 8,444,447 discloses an outboard motor that includes anengine, an exhaust guide, and a catalyst. The engine includes a cylinderand crankshaft. The crankshaft is disposed along a vertical direction.The exhaust guide is arranged to support the engine from below. Thecatalyst is disposed in an interior of the engine. The engine includes acylinder body. The cylinder body includes a housing portion arranged tohouse the catalyst. The cylinder body includes a first exhaust passagethat includes an interior of the housing portion. The catalyst isinserted into the housing portion from below and is sandwiched fromabove and below by the housing portion and the exhaust guide.

U.S. Pat. No. 8,298,026 discloses an outboard motor that includes anengine, an exhaust guide, and a catalyst. The engine includes a cylinderand crankshaft. The crankshaft is disposed along a vertical direction.The exhaust guide is arranged to support the engine from below. Thecatalyst is disposed in an interior of the engine. The engine includes acylinder body. The cylinder body includes a housing portion arranged tohouse the catalyst. The cylinder body includes a first exhaust passagethat includes an interior of the housing portion. The catalyst isinserted into the housing portion from below and is sandwiched fromabove and below by the housing portion and the exhaust guide.

U.S. Pat. No. 8,038,493 discloses a catalyzed exhaust system for anoutboard motor engine that locates its catalyst device in a catalysthousing above an adapter plate which supports the engine and separatesit from the driveshaft housing. The exhaust gas is directed initially inan upwardly direction and then is turned downwardly to provide space forlocation and easy access to the catalyst device. A coolant, such aswater drawn from a body of water, is reversed in direction of flowseveral times in order to advantageously fill certain cooling channelsin an upward direction. In addition, various coolant channels are ventedto remove potential pockets of air in their upper regions.

U.S. Pat. No. 7,954,314 discloses an engine with a cavity so that acatalyst member can be contained within the engine when an engine headportion is attached to an engine block portion. This attachment of theengine head portion and engine block portion, which forms the enginestructure, captivates the catalyst member within the cavity without theneed for additional brackets and housing structures. The cavity ispreferably located above or at the upper regions of first and secondexhaust conduits which direct exhaust upwardly from the engine headportion toward the cavity and downwardly from the cavity within theengine block portion. The first and second exhaust conduits arepreferably formed as integral structures within the engine head portionand engine block portion.

U.S. Pat. No. 7,704,111 discloses an outboard motor that includes amulti-cylinder engine which includes cylinders longitudinally orientedand vertically paralleled in a cylinder block, a cylinder head arrangedat a rearward position of the cylinder blocks, and a crankcase arrangedat a forward position of the cylinder block, the cylinder head having anoutlet of an exhaust port at one side thereof. An exhaust system for theoutboard motor includes an exhaust manifold which communicates theoutlet of the exhaust port with an exhaust outlet opening, the exhaustmanifold including a first exhaust gas passage extending in a verticaldirection for gathering exhaust gas discharged from the outlet of eachexhaust port and a second exhaust gas passage extending in a verticaldirection adjacently to the first exhaust gas passage, and a catalystunit is provided on the way of the second exhaust gas passage.

U.S. Pat. No. 6,662,555 discloses a catalyzer arrangement for an enginethat includes an improved construction that does not require a largespace for furnishing a relatively large volume catalyzer. The engine issurrounded by a protective cowling. A cylinder body of the engine has aplurality of cylinder bores spaced apart from each other. The enginealso has an exhaust manifold to gather exhaust gases from the respectivecylinder bores. An exhaust passage is coupled to the manifold andextends, at least in part, within a space defined between a side surfaceof the cylinder body and the protective cowling. At least one catalyzeris disposed in the exhaust passage.

U.S. Pat. No. 6,511,355 discloses a catalyst exhaust system thatincludes a catalyst housing having an inlet end, an outlet end, and apassage there through. The outlet end includes a valve seat, and a waterjacket surrounds the catalyst housing. A valve housing is in flowcommunication with the outlet end and in flow communication with saidwater jacket to accommodate a valve configured to allow passage ofexhaust gases but prevent water from entering the catalyst housingpassage and reaching a catalyst therein.

U.S. Pat. No. 5,306,185 discloses a marine propulsion device comprisinga propulsion unit including a propeller shaft, a housing including anexhaust gas inlet and an exhaust gas outlet, a catalytic elementsupported in the housing for reorientation from a first orientation to asecond orientation different from the first orientation, and structurefor reorienting the element from the first orientation to the secondorientation.

SUMMARY

This Summary is provided to introduce a selection of concepts that arefurther described herein below in the Detailed Description. This Summaryis not intended to identify key or essential features of the claimedsubject matter, nor is it intended to be used as an aid in limiting thescope of the claimed subject matter.

Exhaust systems are for a marine propulsion device having an internalcombustion engine. In some examples, a catalyst housing has a housinginlet end that receives an exhaust gas flow from the internal combustionengine into the catalyst housing and an opposite, housing outlet endthat discharges the exhaust flow out of the catalyst housing. A catalystis disposed in the catalyst housing. The catalyst has a catalyst inletend that receives the exhaust gas flow and an opposite, catalyst outletend that discharges the exhaust gas flow. A catalyst mantel is on anouter periphery of the catalyst. The catalyst mantel has a mantel inletend and an opposite, mantel outlet end. A radial flange is on at leastone of the mantel outlet end and mantel inlet end. A connector mateswith an inner diameter of the catalyst housing. The radially extendingflange of the catalyst mantel is axially sandwiched between theconnector and a radially inner shoulder of the catalyst housing. Methodsof assembling exhaust systems are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described with reference to the followingFigures. The same numbers are used throughout the Figures to referencelike features and like components.

FIG. 1 is a perspective view of portions of an outboard marinepropulsion device including an internal combustion engine that issupported on an adapter plate.

FIG. 2 is a view of section 2-2 taken in FIG. 1.

FIG. 3 is a view of section 3-3 taken in FIG. 1.

FIG. 4 is a perspective view, partially cutaway, of a catalyst housingfor containing a catalyst for treating exhaust gas flow from theinternal combustion engine.

FIG. 5 is an exploded view of the catalyst housing, a catalyst, anoutlet collector, and a connector that retains the catalyst in thecatalyst housing.

FIG. 6 is a sectional view of the catalyst housing, catalyst, outletcollector and connector.

FIG. 7 is a sectional view of a prior art catalyst housing and outletcollector.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of portions of an outboard marinepropulsion device 10 having an internal combustion engine 12 that issupported on an adapter plate 14. An oil sump 16 extends below theadapter plate 14, as is conventional. The outboard marine propulsiondevice 10 includes an engine block 18 and a cylinder head 20. An exhaustmanifold 22 is attached to the internal combustion engine 12 andreceives exhaust gas flow from the internal combustion engine 12 andconveys the exhaust gas flow ultimately for discharge from the outboardmarine propulsion device 10.

As shown in FIGS. 1-4, a catalyst housing 24 is attached to the exhaustmanifold 22 and receives the exhaust gas flow from the exhaust manifold22. The catalyst housing 24 has a housing inlet end 26 that receives theexhaust gas flow and an opposite, housing outlet end 28 that dischargesthe exhaust gas flow. The catalyst housing 24 can reside in the engineblock 18 or cylinder head 20 or in a separate exhaust component. Acatalyst 30 is disposed in the catalyst housing 24 and is configured totreat the exhaust gases in a conventional manner. The catalyst 30 has anupstream catalyst inlet end 32 that receives the untreated exhaust gasflow and an opposite, downstream catalyst outlet end 34 that dischargesthe treated exhaust gas flow.

An outlet collector 36 is connected to the catalyst housing 24 andreceives the exhaust gas flow from the catalyst housing 24. The outletcollector 36 has a collector inlet end 38 that is engaged with thehousing outlet end 28. In the illustrated example, the collector inletend 38 has a radially inner diameter that is slightly larger than theradially outer diameter of the housing outlet end 28. The collectorinlet end 38 overlaps the housing outlet end 28 at a joint 40. A seal42, which in the illustrated example is an O-ring seal, is disposed atthe joint 40 between the collector inlet end 38 and the housing outletend 28. The seal 42 prevents exhaust gas flow past the joint 40 betweenthe collector inlet end 38 and the housing outlet end 28. It will berecognized by those having ordinary skill in the art that in otherexamples the collector inlet end 38 can have a radially outer diameterthat is smaller than a radially inner diameter the housing outlet end28. In such examples, the housing outlet end 28 would overlap thecollector inlet end 38 at the joint 40.

As shown in FIG. 2, the downstream catalyst outlet end 34 is locatedupstream of the joint 40, as shown in FIG. 3. The outlet collector 36further includes a collector outlet end 44 that discharges the exhaustgases to the engine block 18 of the internal combustion engine 12. Theoutlet collector 36 could be integral to the engine block 18 or adapterplate 14 or connect to the adapter plate 14 for example as a separatemember.

As shown in FIGS. 2-3, a catalyst housing cooling water jacket 46 isdisposed on the catalyst housing 24. An outlet collector cooling waterjacket 48 is disposed on the outlet collector 36. The outlet collectorcooling water jacket 48 extends upwardly to the beginning of the notedjoint 40. The catalyst housing cooling water jacket 46 also extendsdownwardly to the beginning of the noted joint 40, on an opposite sidethereof with respect to the outlet collector cooling water jacket 48.The joint 40 is devoid of a cooling water jacket. In other words, theradially outer periphery of the joint 40 does not have a cooling waterjacket and thus is not water-cooled in the radial direction.

Referring to FIG. 4, first and second bypass conduits 50, 52 each conveycooling water from the outlet collector cooling water jacket 48 to thecatalyst housing cooling water jacket 46. The first and second bypassconduits 50, 52 bypass the joint 40 so that cooling water does not flowalong the noted radially outer periphery of the joint 40. Each of thefirst and second bypass conduits 50, 52 has a first end 54 connected tothe outlet collector cooling water jacket 48 and a second end 56connected to the catalyst housing cooling water jacket 46. In theillustrated example, the second ends 56 are tangentially connected tothe catalyst housing cooling water jacket 46 at fittings 57 so thatcooling water is tangentially introduced to the catalyst housing coolingwater jacket 46 to form a helical cooling water flow in the coolingwater jacket 46 around the catalyst housing 24 and catalyst 30. Thesecond ends 56 are connected to the catalyst housing cooling waterjacket 46 adjacent the joint 40 and seal 42 and angled towards the joint40 and seal 42 so that cooling water flow is directed towards andadjacent to the seal 42 at the joint 40. In the illustrated example, thefirst and second bypass conduits 50, 52 are located on opposite sides ofthe catalyst housing 24. The number and configuration of the bypassconduits can vary from that which is shown.

As shown in FIG. 3, a cooling water pump 58 is configured to pumpcooling water from the body of water in which the outboard marinepropulsion device 10 is operating from upstream to downstream in seriesthrough the outlet collector cooling water jacket 48, the first andsecond bypass conduits 50, 52, and the catalyst housing cooling waterjacket 46. Thereafter, the cooling water flows through a cooling waterjacket 60 on the exhaust manifold 22.

Referring now to FIGS. 5 and 6, the catalyst 30 has a catalyst “can” ormantel 62 on the circumferential outer periphery of the catalyst 30. Thecatalyst mantel 62 has a mantel inlet end 64 and an opposite, manteloutlet end 66. A radial flange 68 is disposed on the mantel outlet end66 and radially extends from the outer periphery of the mantel outletend 66. A connector 70 is configured to mate with the inner diameter ofthe catalyst housing 24 at the housing outlet end 28 in such a mannerthat the radial flange 68 of the catalyst mantel 62 is sandwichedbetween the connector 70 and a radially inwardly extending shoulder 72of the catalyst housing 24.

In the illustrated example, the connector 70 has a threaded radiallyouter peripheral surface 74 that engages with a threaded radially innerperipheral surface 76 on the catalyst housing 24. Rotating the connector70 in one direction with respect to the catalyst housing 24 moves theconnector 70 towards the radially inwardly extending shoulder 72 of thecatalyst housing 24 and clamps the radial flange 68 between theconnector 70 and the radially inwardly extending shoulder 72. Rotatingthe connector 70 in an opposite direction with respect to the catalysthousing 24 moves the connector 70 away from the radially inwardlyextending shoulder 72 of the catalyst housing 24 and releases the radialflange 68 from the connector 70 and the radially inner shoulder 72.Continued rotation allows for removal of the connector 70 from thecatalyst housing 24 so that the catalyst 30 can also be removed from thecatalyst housing 24, as shown in FIG. 5.

In the illustrated example, the threaded radially inner peripheralsurface 76 of the catalyst housing 24 is located at an open end (i.e.housing outlet end 28) of the catalyst housing 24. The connector 70 isin the shape of a ring having an inner passageway 78 that allows exhaustgas flow therethrough. Notches 73 are provided along the inner radiusfor engagement with a tool to manually or mechanically rotate theconnector 70. The inner passageway 78 has a radially inner diameter thatis equal to or larger than a radial diameter of the catalyst outlet end34 so that the connector 70 does not restrict the exhaust gas flowtherethrough/therepast. In one example, the connector 70 can be made ofbrass and the catalyst housing 24 can be made of aluminum so that theconnector 70 and catalyst housing 24 undergo similar thermal expansionand contraction during changes of temperature.

The catalyst inlet end 32 and the mantel inlet end 64 are separated fromthe catalyst housing 24 so that the catalyst inlet end 32 and mantelinlet end 64 are free to thermally expand and contract due to changes intemperature in the exhaust system. The seal 42 that is disposed betweenthe collector inlet end 38 and the housing outlet end 28 radiallyoverlaps with the connector 70, as shown in FIG. 6. As explained hereinabove, the collector inlet end 38 and housing outlet end 28 are devoidof a cooling jacket.

The present disclosure thus provides methods of assembling an exhaustsystem for an outboard marine propulsion device 10 having an internalcombustion engine 12. In certain examples, the methods can includeproviding a catalyst housing 24 having a housing inlet end 26 thatreceives an exhaust gas flow from the internal combustion engine intothe catalyst housing 24 and an opposite, housing outlet end 28 thatdischarges the exhaust gas flow out of the catalyst housing 24. Themethods can further include disposing a catalyst 30 in the catalysthousing 24, the catalyst 30 having a catalyst inlet end 32 that receivesthe exhaust gas flow and an opposite, catalyst outlet end 34 thatdischarges the exhaust flow. A catalyst mantel 62 can be disposed on anouter periphery of the catalyst 30. The catalyst mantel 62 has a mantelinlet end 64 and an opposite mantel outlet end 66. A radial flange 68 ison the mantel outlet end 66. The method further can include mating aconnector 70 with an inner diameter of the catalyst housing 24 such thatthe radial flange 68 of the catalyst mantel 62 is sandwiched between theconnector 70 and a radially inwardly extending shoulder 72 of thecatalyst housing 24. An outlet collector 36 can be provided thatreceives the exhaust gas flow from the housing outlet end 28. The methodcan include engaging a collector inlet end 38 of the outlet collector 36with the housing outlet end 28 so that the collector inlet end 38overlaps with the housing outlet end 28, with a seal being disposedbetween the collector inlet end 38 and the housing outlet end 28.

Through research and development, the present inventors have endeavoredto provide improved cooling systems and exhaust systems for outboardmarine propulsion devices. The present inventors have determined thatoutboard marine propulsion devices preferably are water cooled to keepmetal temperatures low. A common method of doing this is water-jacketingthe exhaust manifold and other passages. However cooling water jacketshave been found by the present inventors to disadvantageously take upadditional space and cause sealing challenges at gasketed joints. Sincegasketed joints require additional space for gaskets and fasteners, thepackaging impact of water jacketed exhaust passages has been found mostchallenging at gasketed joints.

FIG. 7 depicts a conventional manner in which exhaust joints are watercooled. Two O-rings A, B are utilized, O-ring A seals the exhaustconduits and O-ring B seals the water jackets. Radially sealing O-ringjoints typically are tolerant of axial movement of the joint (e.g.movement due to tolerances, thermal growth, or vibration). Radiallysealing O-rings are also slightly forgiving of angular misalignments andeccentricity. The present inventors have found that this two O-ringdesign is a robust joint, but is not a compact design.

The present inventors have also endeavored to provide a more compactarrangement without interfering with surrounding components of theoutboard marine propulsion device 10 including the exhaust runners, cowland spark plugs. Through research and development, it was found that aface seal would fit in the requisite packaging space, but would notprovide the tolerance to axial and angular misalignment that was neededfor a robust joint. The present inventors developed the presentlyillustrated solution that includes a single O-ring joint, where theO-ring only seals the exhaust. To avoid overheating of the materialsincluding the aluminum castings, silicone O-ring, water is plumbed viathe first and second bypass conduits 50, 52 directly above and below thesingle O-ring.

The present inventors have also found a drawback of O-ring joints,including the fact that they must be circular, which limits designflexibility. To use a conventional two O-ring joint (shown in FIG. 7),the outer O-ring would need to be large enough to allow water to passbetween it and the exhaust passages, but at that size it would interferein the areas explained herein above. By not using the outer O-ring andexternally plumbing the water, design freedom was afforded to place theplumbing only where there was available space.

As FIGS. 1-6 show, the single O-ring advantageously does not make thejoint any larger than the adjacent areas. The externally plumbed wateradequately cools the metal and O-rings. To help assure proper cooling,the water that reenters the system can be supplied in tangential to thewater jacket, therefore creating good circular flow adjacent to theO-ring. The cooling water flows upstream to downstream up the outletcollector, through the externally plumbed water hoses, and into themanifold cooling jacket.

The embodiment shown in the drawings depicts the joint 40 locatedbetween the collector inlet end 38 and the housing outlet end 28;however the concepts of the present disclosure are not so limited. Forexample, the joint 40 can be located at the housing inlet end 26 and beformed between a downstream engagement end of an exhaust conduit, forexample of the exhaust manifold 22. Just like the arrangement shown inthe drawings, this example would include a joint that is devoid of acooling water jacket and provide the same advantages described hereinabove.

The present disclosure thus contemplates exhaust systems for a marinepropulsion device 10 having an internal combustion engine 12. Theexhaust systems can include a catalyst housing 24 having a housing inletend 26 that receives an exhaust flow from the internal combustion engine12 and an opposite housing outlet end 28 that discharges the exhaustflow. A catalyst 30 is disposed in the catalyst housing 24. An exhaustconduit, which can be a member of the exhaust manifold 22 or an outletcollector 36 that receives the exhaust flow from the catalyst housing24, conveys exhaust gases to the catalyst housing 24 or from thecatalyst housing 24. The exhaust conduit includes an engagement end, forexample collector inlet end 38, that is engaged with the catalysthousing 24 in such a manner that one of the engagement end and thecatalyst housing 24 overlaps the other of the engagement end and thecatalyst housing 24 at a joint, for example joint 40. A seal, such asthe O-ring seal 42 is disposed at the joint between the engagement endand the catalyst housing 24. The joint, as mentioned herein above, canbe devoid of a cooling water jacket.

Besides the packaging benefits, this arrangement has also been found bythe present inventors to provide advantages over the conventional twoO-ring joint design shown in FIG. 7, including no water to exhaust leakpath if the O-ring fails or gets damaged, and no water boiling in tightclearances around the exhaust O-ring, therefore limiting corrosion.

In the illustrated example, the catalyst 30 is installed in the catalysthousing 24 on the exhaust manifold 22. The catalyst 30 is installedaxially into the catalyst housing 24 retained via the connector 70,which in the illustrated example is a large diameter externally threadednut (i.e. spanner nut). This arrangement could also work if the catalyst30 was retained in a different component, such as if the catalysthousing 24 were integral with the cylinder head 20 or engine block 18.Advantageously, this example allows for thermal expansion of thecatalyst 30 and mantel 62 at the inlet end, and securely retains thecatalyst 30 and mantel 62 at the outlet end. The connector allows foreasy assembly and disassembly from the catalyst housing.

In the above description, certain terms have been used for brevity,clarity, and understanding. No unnecessary limitations are to beinferred therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued. The different systems and method steps described herein maybe used alone or in combination with other systems and methods. It is tobe expected that various equivalents, alternatives and modifications arepossible within the scope of the appended claims. In alternate examples,the radial flange 68 of the catalyst mantel 62 can be located on themantel inlet end 64 instead of the mantel outlet end 66. In suchexamples, the connector 70 can be configured to mate with the upstreamcatalyst housing inlet end 26 instead of the downstream, catalysthousing outlet end 28. This embodiment allows for installation of thecatalyst housing inlet end 26 prior to attachment to the exhaustmanifold 22.

1-20. (canceled)
 21. An exhaust system for a marine propulsion devicehaving an internal combustion engine, the exhaust system comprising: anexhaust conduit having a exhaust conduit inlet end that receives anexhaust gas flow from the internal combustion engine and an opposite,exhaust conduit outlet end that discharges the exhaust gas flow; anoutlet collector that receives the exhaust gas flow from the exhaustconduit, wherein the outlet collector comprises a collector inlet endthat is engaged with the exhaust conduit outlet end such that one of thecollector inlet end and exhaust conduit outlet end overlaps with theother of the collector inlet end and exhaust conduit outlet end at ajoint; and a seal disposed at the joint between the collector inlet endand the exhaust conduit outlet end; wherein the joint is devoid of acooling water jacket.
 22. The exhaust system according to claim 21,further comprising an exhaust conduit cooling water jacket disposed onthe exhaust conduit.
 23. The exhaust system according to claim 21,further comprising an outlet collector cooling water jacket disposed onthe outlet collector.
 24. The exhaust system according to claim 21,wherein the collector inlet end has a radially inner diameter that islarger than a radially outer diameter of the exhaust conduit outlet endand wherein the collector inlet end overlaps the exhaust conduit outletend at the joint.
 25. The exhaust system according to claim 21, furthercomprising an outlet collector cooling water jacket on the outletcollector, an exhaust conduit cooling water jacket on the exhaustconduit, and at least one bypass conduit that conveys cooling water fromone of the outlet collector cooling water jacket and exhaust conduitcooling water jacket to the other of the outlet collector cooling waterjacket and exhaust conduit cooling water jacket.
 26. The exhaust systemaccording to claim 25, wherein the at least one bypass conduit bypassesthe joint so that cooling water does not flow along a radially outerperiphery of the joint.
 27. The exhaust system according to claim 25,wherein the at least one bypass conduit comprises a first end connectedto the outlet collector cooling water jacket and a second end connectedto the exhaust conduit cooling water jacket.
 28. The exhaust systemaccording to claim 27, wherein at least one of the first and second endsare tangentially connected to one of the respective outlet collectorcooling water jacket and exhaust conduit cooling water jacket so thatcooling water is introduced to the one of the respective outletcollector cooling water jacket and exhaust conduit cooling water jacketin a helical water flow.
 29. The exhaust system according to claim 27,wherein the at least one of the first and second ends is connected tothe one of the respective outlet collector cooling water jacket andexhaust conduit cooling water jacket adjacent the joint, so that thewater helical flow is adjacent the seal.
 30. The exhaust systemaccording to claim 27, wherein the at least one bypass conduit comprisesa first bypass conduit and a second bypass conduit that are located onopposite sides of the exhaust conduit.
 31. The exhaust system accordingto claim 21, wherein the outlet collector comprises a collector outletend that discharges exhaust gases.
 32. The exhaust system according toclaim 31, wherein the collector outlet end discharges exhaust gases to acylinder block of the internal combustion engine.
 33. An exhaust systemfor a marine propulsion device having an internal combustion engine, theexhaust system comprising: a exhaust conduit having a conduit inlet endthat receives an exhaust gas flow from the internal combustion engineand an opposite, conduit outlet end that discharges the exhaust gasflow; an outlet collector that receives the exhaust gas flow from theexhaust conduit, wherein the outlet collector comprises a collectorinlet end that is engaged with the conduit outlet end, wherein one ofthe collector inlet end and conduit outlet end overlaps with the otherof the collector inlet end and conduit outlet end at a joint; and a sealdisposed at the joint between the collector inlet end and the conduitoutlet end; an outlet collector cooling water jacket on the outletcollector, a exhaust conduit cooling water jacket on the exhaustconduit, and at least one bypass conduit that conveys cooling water fromone of the outlet collector cooling water jacket and exhaust conduitcooling water jacket to the other of the outlet collector cooling waterjacket and exhaust conduit cooling water jacket; wherein the at leastone bypass conduit bypasses the joint so that cooling water does notflow along a radially outer periphery of the joint; and a cooling waterpump that pumps cooling water from upstream to downstream through theoutlet collector cooling water jacket, at least one bypass conduit, andexhaust conduit cooling water jacket.
 34. The exhaust system accordingto claim 33, wherein the cooling water pump pumps the cooling water inseries through the outlet collector cooling water jacket, the at leastone bypass conduit and then the exhaust conduit cooling water jacket.35. The exhaust system according to claim 34, wherein the at least onebypass conduit comprises a first end connected to the outlet collectorcooling water jacket and a second end connected to the exhaust conduitcooling water jacket.
 36. The exhaust system according to claim 35,wherein at least one of the first and second ends are tangentiallyconnected to one of the respective outlet collector cooling water jacketand exhaust conduit cooling water jacket so that cooling water isintroduced to the one of the respective outlet collector cooling waterjacket and exhaust conduit cooling water jacket in a helical flow. 37.The exhaust system according to claim 36, wherein the at least one ofthe first and second ends is connected to the one of the respectiveoutlet collector cooling water jacket and exhaust conduit cooling waterjacket adjacent the seal so that the helical flow is adjacent the seal.38. The exhaust system according to claim 33, wherein the outletcollector comprises a collector outlet end that discharges exhaustgases.
 39. The exhaust system according to claim 38, wherein thecollector outlet end discharges exhaust gases to a cylinder block of theinternal combustion engine.
 40. An exhaust system for a marinepropulsion device having an internal combustion engine, the exhaustsystem comprising: a exhaust conduit having a conduit inlet end thatreceives an exhaust gas flow from the internal combustion engine and anopposite, conduit outlet end that discharges the exhaust gas flow; anexhaust conduit that conveys exhaust gases to the exhaust conduit orfrom the exhaust conduit; wherein the exhaust conduit comprises anengagement end that is engaged with the exhaust conduit, wherein one ofthe engagement end and the exhaust conduit overlaps the other of theengagement end and the exhaust conduit at a joint; and a seal disposedat the joint between the engagement end and the exhaust conduit; whereinthe joint is devoid of a cooling water jacket.